Magnetic resonance imagining (MRI) has become a recognized and very useful tool for the diagnosis of numerous disease processes and pathologies of the human body, relying on the natural abundance of hydrogen in the body and its nature to precis, or spin, about in quasi-alignment with the strong magnetic field of MRI. MRI provides three-dimensional images of internal structures of a patient (e.g., human or animal). The internal structures may be bone structures, soft tissue (tendons, ligaments, and the like), and organs. MRI is a non-invasive diagnostic test that may determine the state of a disease (e.g., chronic obstructive pulmonary disease (COPD), cancer, and the like), or determine an abnormality in an internal structure (tendon rupture, stress bone fractures, and the like) without subjecting a patient to an invasive procedure, such as a needle biopsy or exploratory surgery.
Many conventional MRI systems are configured for transmitting and receiving radio frequency (RF) at a single RF (e.g., mononuclear systems). Such conventional MRI systems typically transmit and receive RF at the frequency of hydrogen, as this is the most common nuclei in a patient to image. However, hydrogen is not the only nuclei which recesses and can give off a signal in an MRI system, and certainly isn't the only nuclei occurring in the human body. Calcium, carbon, and phosphorous are three others occurring in sufficient quantities that have been exploited to generate signals of clinical interest from the body in a process known as MR spectroscopy, and, of late, actual images based upon the amount and bonding of such nuclei in the body.
Each nuclei has its own precessional frequency that is associated with the magnetic field strength of the MRI system according to the formula ω=σBo, in which ω is the precessional frequency f times 2π, or the radian frequency, σ is the unique gyromagnetic ratio of the element in units Hz/Tesla, and Bo is the strength of the magnetic field in units Tesla. The most commonly installed and operable field strengths are 1.5 Tesla and 3 Tesla systems. While these systems are described in terms of 1.5 or 3 Tesla, their actual magnetic field strength may vary according to different manufacturers. MRI systems typically are designed to provide easy and temporary connection for various MRI antennae designed to improve the signal quality from different human anatomies; hence, they are anatomically specific antennae which the MRI operator places upon these various anatomies and then connects the antennae to the common ports on the MRI system. These antennae now utilize multiple resonators contained within which connect to multiple receiver inputs on the receiver port of the MRI system and, similarly, anatomic specific transmit antennae connect to the transmit output port so as to focus the transmit energy to a smaller local anatomy versus the entire body, which is the purpose of the MRI system's built-in body transmit/receive coil.
There is an increasing need in clinical MRI which relies upon the use of nuclei, other than hydrogen, occurring naturally within the body, or those temporarily injected or inhaled. Only imaging at the single RF of hydrogen does not always provide sufficient imaging of a patient. For example, when imaging a patient's lungs it is at times preferable to have spatial and temporal imaging, which requires imaging nuclei at a first frequency (e.g., hydrogen) and nuclei at a second frequency (a nuclei other than hydrogen, such as fluorine, xenon, and the like). Flourine-19 is an example of such an element that can be inhaled in an inert form, mixed with air, and due to its natural resonance in MRI, can be exploited to generate images of the lungs and associated parenchyma. However, a mononuclear MRI system is not capable of transmitting and receiving at the second frequency.
A major hurdle preventing more common use of other nuclei is the significant expense associated with making MRI systems able to operate at dual or multiple frequencies associated with different nuclei. This expense is largely due to the significant additional hardware and firmware associated with duplicating the radio frequency (RF) transmit and receiver chains for each additional frequency, or providing more expensive broad-band chains that can operate at substantially different frequencies. Primarily for this reason, most MRI systems are manufactured and installed which operate on a singular frequency—the precessional frequency of hydrogen.
Additionally, conventional MRI systems that have the ability to generate an MRI excitation signal and receive from at least two nuclei frequencies (e.g., a multinuclear capable system) do not always have the ability to switch the frequency for receiving and transmitting contemporaneously when the patient is undergoing an MRI scan. This contemporaneous switching is typically limited by the receiving and transmitting coils of the MRI system. Therefore, in order to upgrade a multinuclear capable system, a transmission coil and receiving coil must be configured to allow the MRI system to transmit and receive at at least two nuclei frequencies.
Some conventional multinuclear capable MRI systems further include a multinuclear transmit body coil. However, these multinuclear capable MRI systems with a multinuclear transmit body coil, typically include multi-channel receiver coils. The multi-channel receiver coils include multiple resonators that typically only have the ability to receive at a frequency for a single nucleus. To configure a multinuclear capable MRI system to receive and transmit at a second frequency, the patient must be removed and a separate, distinct receiver coil having resonators that receive RF from a second, distinct nucleus must be placed on the patient. This causes positioning changes and the ability to spatially compare the images of the first nucleus frequency and the second nucleus frequency may be lost.
Finally, the minority of conventional multinuclear MRI systems that have the ability to contemporaneously switch frequencies that are transmitted and received utilize an intermediate frequency in the receiving coil. Such multinuclear MRI systems utilize a resonator in a receiver coil that does not include a tuned preamplifier, such that the signal received by the resonator is converted to an intermediate frequency prior to amplification. In such a multinuclear MRI system, the intermediate frequency must be converted to MRI system receiver frequency. This two-step frequency conversion, from the frequency of a nucleus to an intermediate frequency, and from the intermediate frequency to the MRI system receiver frequency requires a specialized receiver for the two-step conversion, or alternatively the MRI system receiver, itself, must be modified to accept and process the intermediate frequency generated by the first step of the conversion. This means that either the multinuclear MRI system must come with such a specialized receiver, or that the multinuclear system must further be retrofitted for a receiver with the two-step conversion, or, alternatively, the modification of the existing MRI system receiver increases the complexity of the MRI system, increases the complexity of converting a mononuclear system, and increases the cost associated with each.
Therefore, it would be desirable to have an MRI coil package that may be used to alter a mononuclear MRI system to a multinuclear MRI system that may contemporaneously switch between transmitting and receiving RF at a first nuclei and a second nuclei frequency, in which the receiver coil of the MRI coil package has one or more resonators that receive at at least two frequencies from a first nuclei and a second nuclei. It would be further desirable to have an MRI coil package that may alter a multinuclear capable MRI system to a multinuclear functional MRI system, which may contemporaneously switch between transmitting and receiving RF at a first nuclei and a second nuclei frequency, in which the receiver coil of the MRI coil package has one or more resonators that receive at at least two frequencies from a first nuclei and a second nuclei. Further, it would be desirable that the MRI coil package alter the mononuclear MRI system and the multinuclear capable MRI system to a multinuclear system without the use of an intermediate frequency. Finally, it would be desirable that the MRI coil package provide spatial and temporal imaging of a patient from at least two RF.